Mechanochemical devulcanization of natural rubber vulcanizate by dual function disulfide chemicals

Abstract

Devulcanized natural rubber (DeVulcNR) was produced from NR vulcanizate in an open roll mixing mill by using bis(3-triethoxysilyl propyl) tetrasulfide (TESPT), a novel devulcanizing agent. The versatility of the proposed devulcanizing agent TESPT is that it acts as a devulcanizing agent during devulcanization and as a coupling agent during dispersion of silica filler in devulcanize rubber compound. The extent of devulcanization was monitored through the measurements of sol content, gel content, crosslink density, molecular weight between crosslinks, Mooney viscosity of devulcanized rubber and degree of devulcanization as a function of devulcanization time and the concentration of TESPT. The study of extent of devulcanization by monitoring the above mentioned parameters clearly indicate that the optimum concentration of TESPT is 6 mL. Therefore, for further study DeVulcNR is prepared using 6 mL TESPT and designated as DeVulcNR-6 to optimize the devulcanization time. Determination of the fraction of immobilized polymer chains of DeVulcNR-6 by differential scanning calorimetry (DSC) study indicates that with sol content the fraction of immobilized polymer chains decreases due to increasing molecular weight between crosslinks. To get an idea about the application of DeVulcNR in product formulation revulcanization characteristics in the presence of silica filler were studied. The optimum cure time decreases whereas cure rate increases with devulcanization time. The mechanical properties e.g., modulus at 50% and 100% elongation, tensile strength and elongation at break increases with devulcanization time upto 40 min. To see the reinforcement of silica filler, the mechanical properties of ReVulcNR-6 with silica is compared to that of the ReVulcNR-6 without silica. The mechanical property and thermal behavior data clearly indicates that the optimum time for devulcanization is 40 min. Scanning electron microscopy (SEM) studies further show the coherency and homogeneity of DeVulcNR-6 in the revulcanizate when devulcanization is carried out by optimum TESPT concentration 6 mL and devulcanization time 40 min.